The present invention relates generally to electronic image enhancement and recovery, and more particularly, to a method and apparatus for collecting defect data from documents and films for use in removing defects from an image.
The field of electronic imagery has long aimed at capturing and reproducing an accurate digital representation of an image as it currently exists on a physical medium, such as a document or film. Often, however, such digital representations appear distorted. One cause of such distortions is a defect in an image-capturing system component. For example, the translucent document-scanning surface or xe2x80x9cplatenxe2x80x9d in an electronic document image scanner might contain scratches or other optical path obstructions. More frequently, however, distortions result from factors outside the image-capturing system. For example, a photograph, film or other medium in which an image is contained might itself become scratched or otherwise distressed or deformed despite even the most careful handling. In addition, foreign matter, such as a hair or dust, might become deposited on the physical medium. Thus, even where an image captures what it xe2x80x9csees,xe2x80x9d distortions might yet occur.
Traditionally, the above distortions have been largely ignored in favor of increasingly accurate image capturing and reproduction. FIG. 1, for example, broadly depicts a conventional flatbed document image scanner or xe2x80x9cflatbed scanner.xe2x80x9d (For clarity, electronic data processing and storage elements have been removed.) As shown, scanner 100 includes platen 101 and, below platen 101, light source 103, mirror 105, and sensor 107. Sensor 107 further includes lens 107a and image sensor 107b. Image sensor 107b is typically a linear or a multi-linear sensor such as a charge-coupled device (xe2x80x9cCCDxe2x80x9d). However, other image-capturing devices might use other sensor types. For example, a drum scanner might utilize a point or multi-point sensor, such as a photomultiplier tube or xe2x80x9cPMT.xe2x80x9d
Operationally, an original document is positioned on platen 101 such that the source image faces platen 101. Light source 103 is then illuminated, and source image 121a is scanned. During scanning, light source 103 directs light toward and causes reflections from a region of source image 121a. Mirror assembly 105 then re-directs or xe2x80x9cfoldsxe2x80x9d the reflected light to lens 107a, which focuses received light onto image sensor 107b. Next, sensor 107b converts the focused light to electrical signals. The electrical signals are then converted to digital image data using an analog-to-digital (A/D) converter (not shown), and the digital image data is further processed and stored. While multiple sensor arrays might be utilized, the whole of image 121a is typically scanned in successive regions, thereby limiting the number of sensors needed. Such region-to-region scanning is typically accomplished by sequentially moving mirror assembly 105 and sensor 107. As mirror assembly 105 is moved, sensor 107 receives reflected light from successive regions of document 121. The image is then reconstructed from the image data during image processing.
To assure image-capturing accuracy, flatbed scanners and other optical image-capturing systems have continually refined the nature of the light source 103, mirror 105""s position, and sensor 107. For example, a document, film, or other subject must be sufficiently and evenly lighted to allow capturing of image reflections from source document 121 without causing glare. Therefore, a single, typically fluorescent light source is provided. In addition, the mirror is positioned such that glare is avoided and both primarily bright and primarily dark images will be accurately captured. Therefore, each sequential mirror position is set such that light is directed from the light source to the image at a first angle and is then reflected (from the image) to a sensor at a significantly different second angle. More specifically, image clarity is assured in most devices by providing first and second angles which differ by at least 45 degrees. The resolution and optical efficiency of the sensor have also been continually improved.
Traditionally, image-capturing devices have not provided image distortion (or xe2x80x9cdefectxe2x80x9d) detection, let alone correction. Rather, their objective was strictly directed at image-capturing accuracy. Therefore, the above arrangement was considered optimal for its intended purpose. Unfortunately however, such an arrangement also produces optical effects that not only fail to provide for defect detection, but also impose an optical environment that runs counter to such an objective.
While recent image-capturing devices attempt to detect image defects, such attempts depend on the image-data accuracy provided by the above image-scanning method. In such devices, an image is scanned in the traditional manner. Scanned image data is then reviewed in much the same way that a human observer might look for defects in a reproduced image. More specifically, after capturing image data, mathematical algorithms are used to search the image data for extraneous dark spots that might be indicative of image defects. Upon locating such dark spots, the algorithms determine whether the located spots are likely indicative of an image defect, determine the graphic features of selected defects, and attempt correction. Unfortunately, defects are difficult to separate from other image data, let alone correct, by reviewing the captured image data in this manner.
A system and method that corrects defects in an image is described in U.S. Pat. No. 5,266,805, entitled xe2x80x9cSystem and Method For Image Recoveryxe2x80x9d, and is assigned to International Business Machines (xe2x80x9cIBMxe2x80x9d). The invention teaches sequentially transmitting through film red, green, blue and infrared light, and then performing correction by dividing out defects using the resulting image data, or alternatively, using an automated fill-in algorithm.
Further methods and apparatus that provides for detecting image defects are described in co-pending U.S. application Ser. No. 08/999,421, filed Dec. 29, 1997, entitled Defect Channel Nullingxe2x80x9d and U.S. application Ser. No. 09/156,271, filed Sep. 16, 1998, entitled Method And Apparatus For Capturing Defect Data From Documents And Films, both commonly owned by the assignee of the present application.
The contents of U.S. Pat. No. 5,266,805, U.S. application Ser. Nos. 08/999,421 and 09/156,271 are hereby incorporated by reference as if repeated verbatim immediately hereinafter.
While the above prior patent and patent applications provide for defect handling in image-capturing systems, the new technological area of defect detection and correction remains subject to such a further advance as will become apparent in the discussion that follows.
Accordingly, there remains a need in the art for a system that enables defect data to be accurately captured for use in removing defects from an image.
According to a first aspect, the invention provides a positional relationship between system elements such that defects within an image are rendered more apparent. According to a second aspect, the invention provides for identifying defects within an image. According to still further aspects, the invention provides for rendering defects more apparent and identifying such defects within an image-capturing device. Advantageously, the present invention enables defects to be clearly captured, identified and corrected. In addition, the invention facilitates the use of various light sources and/or mechanisms within an image-capturing device for defect detection and/or correction in accordance with the constraints of a particular application.
The present invention provides a method and apparatus for image-capturing devices, such as scanners, to accurately identify defects in objects. The objects can be the physical images to be captured or elements of the image-capturing devices such as the platen and mirrors. The image-capturing devices can then use this defect information to remove defects from captured images.
The present invention more specifically provides a method and apparatus for recording defect data, such that light is detected at an angle roughly equal to the angle at which the light is directed to the object, i.e. where the angle of reflection roughly equals the angle of incidence. The present invention recognizes that light reflected from surface defects has a wider diffusion and thus a lower amplitude than light reflected from the surface of the object itself. The information obtained regarding the defects can be used by image-capturing devices in software applications with mathematical algorithms to enhance captured images by removing these defects.
In one embodiment, an image-capturing system preferably provides, within a flatbed scanner, light sources for image and defect scanning, a scanning controller and a defect processor. The controller regulates illumination of the light sources and movement of a conventionally provided mirror such that image information and defect data are separately captured. The image is then conventionally processed. The defect data is separately processed to identify and enable removal of defects. Preferably, reflected light is separately utilized for capturing a source image and for capturing image and system defects. During a first (xe2x80x9cimage-scanningxe2x80x9d) cycle, the controller illuminates the first light source and establishes a positional relationship among system elements for capturing the source image. During a second (xe2x80x9cdefect-scanningxe2x80x9d) cycle, the controller illuminates the second light source and establishes a positional relationship among system elements for optimally capturing defects, thereby producing defect data. Processing of the image-scan data and defect-scan data is further conducted by an image processor and defect corrector respectively in order to separately reconstruct the image and correct defects. Defect data is preferably processed in a manner corresponding to a relative intensity of captured reflected light.
In a further embodiment, a single light source is preferably utilized within a single image and defect scan cycle.
A still further embodiment provides a film scanner in which defect detection and correction are enabled in accordance with the invention.
The present invention also teaches using software to measure the maximum amplitude of the upward light wave reflected from the surface of the object at this angle. The software then calculates a threshold value for defects, based on a percentage of this maximum amplitude, and identifies as defects those areas on the object that reflect light with an amplitude at or below the threshold value.